1) Field of the Invention
The present invention relates to a holography system for a real-time reconstruction of a three-dimensional image of an object.
2) Description of the Related Art
As well known, in a holography system using a photographic technique, an object light wave and a reference light wave, derived from a coherent light such as a laser, interfere with each other on a photographic film to thereby cause an interference-fringe pattern, and that pattern is then recorded as a latent image on a photographic film. Thereafter, by developing and fixing the photographic film, a negative or hologram on which the interference-fringe pattern is recorded as a visual image can be obtained. When an reference light wave is incident on the hologram, the above-mentioned object light wave is reproduced as a diffracted light wave, whereby a three-dimensional image of an object, from which the object light wave derives, can be reconstructed. As is also well known, in a holography system using a photographic technique, the three-dimensional image of an object cannot be reconstructed in real-time, because the hologram is obtained after the photographic film is developed and fixed.
A real-time holography system is disclosed in "APPLIED OPTICS", Vol. 11/No. 5, May 1971, pages 1261 to 1268, by R. J. Doyle and W. E. Glenn. In this real-time holography system, an interference-fringe pattern caused by an object light wave and a reference light wave is recorded by an image pickup device, an image of the interference-fringe pattern is converted into a video signal, and the image of the interference-fringe pattern is then reconstructed on a transparent thermoplastic medium on the basis of the video signal. In particular, the transparent thermoplastic medium is formed of a transparent electrode and has a transparent thermoplastic layer coated thereon. The transparent thermoplastic layer is scanned with an electron beam carrying the video signal, so that an electric charge distribution corresponding to the interference-fringe pattern is formed on the thermoplastic layer, and thus an electrostatic force acts on the thermoplastic layer in response to the electric charge distribution. At the same time, the thermoplastic layer is electrically heated, whereby a surface of the thermoplastic layer is deformed and grooves and ridges are formed thereon to reproduce the interference-fringe pattern, and thus a phase hologram is produced on the thermoplastic layer surface. Thereafter, when a coherent light wave is incident on the phase hologram, a three-dimensional image of an object, from which the object light wave derives, can be reconstructed.
In this conventional real-time holography system, some time is required until the deformation of the thermoplastic layer surface is completed, and thus, in this sense, it cannot be said that the three-dimensional image is reconstructed in real-time. Also, it is very difficult and costly to reconstruct a three-dimensional motion picture by utilizing the conventional system, because a plurality of transparent thermoplastic mediums must be prepared, and because these mediums must be successively moved to a three-dimensional image reconstruction location at which the reference light wave is incident on the transparent thermoplastic medium. Furthermore, the conventional system has a drawback in that the transparent thermoplastic medium is quickly deteriorated; i.e., the reproduction of the intereference-fringe pattern on the transparent thermoplastic medium can be performed only several thousand times.